Method of making coated paper of low gloss and improved ink holdout



NOV. 26, 1968 c5 H, RASMUSSEN ET AL 3,413,139

METHOD OF MAKING COATED PAPER OF LOW GLOSS AND IMPROVED INK HOLDOUT Filfid D60. 30, 1964 2 Sheets-Sheet l MAIN DRYER SECTION MACH PRESS comma DRYER COATER SECTION SIZE PRESS COATING mm DRYER SECTION MACH MASSEY CAL. comm comma DRYER SECTION MASSEY comma INVENTORS GEORGE H. RAsMussEN James R su A'r'rvs,

SUPERCALENDER\NG Nov. 26, 1968 G. H. RASMUSSEN ET AL 3,413,139

METHQD OF MAKING COATED PAPER OF LOW GLOSS AND IMPROVED INK HOLDOUT 2 Sheets-Sheet 2 Filed Dec. 30, 1964 N 8 5w m R o W M a A T S U N a ER F2mZwuZ mm wzrEou m8. wH 5 W I E E 7 G M WD 4Q )3 32 5 20 l M m $58 qmw E 0 u 3 o 9 G .5 u k 052:: W 5N .EZD .QN .A Ba -Ez QN O vw 0 0 O mN @N :23 cm. dam 52. O O 3 .8 on 9 29.5mm mi 62: zoiumm 1E 51: m 55.0 93 O 0 $25 Q.

United States Patent 3,413,139 METHOD OF MAKING COATED PAPER OF LOW GLOSS AND IMPROVED INK HOLDOUT George H. Rasmussen, Wisconsin Rapids, and James A.

Rush, Stevens Point. Wis., assignors to Consolidated Papers, Inc., Wisconsin Rapids, Wis., a corporation of Wisconsin Filed Dec. 30, 1964, Ser. No. 422,207 9 Claims. (Cl. 117-64) ABSTRACT OF THE DISCLOSURE Method of making coated paper of low gloss and improved ink holdout character comprising applying to one or both surfaces of a forwardly moving paper web at least one coat of an aqueous mineral pigment and binder-containing aqueous coating composition, drying said coating after application, supercalendering said coated web to impart gloss thereto, applying thereover a final aqueous mineral pigment and binder-containing coating composition, doctoring the last coating before drying, drying it and recovering the coated web as a product of the process in the absence of further supercalendering.

This invention relates to the production of coated paper of novel surface character.

More particularly the present invention relates to the production of paper eminently suitable for offset printing and characterized by a low gloss and improved ink holdout.

The paper of the present invention is further characterized by its smooth or level character resulting from application to the paper web of two or more successive layers of aqueous coating composition containing mineral pigment and binder, and the leveling of at least the last applied or top coating while web by doctoring means such as a flexible blade disposed immediately at or spaced from the point of coating application, or by an air jet extending across the sheet, also known as an air knife or air brush.

In producing a low gloss, semigloss, or dull coated paper for oifset printing, it is customary to first coat the web with a pigmented coating, either singularly or by successive means, until fully coated and then use only machine calendering which leaves a nonglossy surface, which may, in fact, be quite rough and with poor ink holdout characteristics, or develop the desired surface finish by means of special finishing techniques using special and costly calendering equipment. In accordance with the present invention, the final desired finish is obtained by producing a desired undergloss by means of conventional supercalendering of the first or prime coated web and then applying an over or dulling coat that has been leveled by means of doctoring by flexible blade or air knife. The Web is then given no subsequent or after additional treatment. By this method it is possible to employ conventional equipment, procedures and coating compositions in a novel sequence, wherein no special equipment is required.

The objects of the present invention are accomplished by subjecting the paper web to supercalendering after the first or prime coating has been applied and dried, or after an intermediate coating has been applied and dried in such cases where an intermediate coating is employed, and prior to the application of the final or top coating. The aforesaid coated sheet is supercalendered to a desirable surface gloss, such as a TAPPI 75 specular gloss, of between 25 and 60, with the preferred range being 35 to 45, prior to final covering by blade or air knife coating means.

The first or prime coating can be applied by a horizontally or vertically disposed size press, by transfer or imprint roll coating with a metered amount of coating composition, or by blade coating wherein a Wet newly applied coating composition is doctored by means of a flexible metal blade or by a jet of air. When an intermediate coating is employed it can be any of the foregoing, and the final or top coat is preferably applied by the technique employing doctoring as aforesaid.

The supercalendering practiced prior to applying the top coating employs the normal pressure and number of nips used on conventional supercalendering equipment, such as described in Paper Trade Journal, Nov. 18, 1964, The Modern Calender and Supercalender, p. 36. In the supercalender the sheet passes through a number of nips which are formed by adjacent metal and resilient fiber rolls, as opposed to machine calendering where all rolls are normally metallic. The sheet may or may not be steamed during the supercalendering operation.

By the present method it is possible to produce coated paper in the 15 to 20 range of TAPPI specular gloss with much greater holdout than commercial grades now on the market in the 30 75 TAPPI specular gloss range.

The objects and advantages of the present invention and its details and economies will be further apparent from a consideration of the following specificaiton and accompanying drawings, wherein:

FIG. 1 is a diagrammatic arrangement of a typical apparatus suitable for applying a first or prime coating to a paper web.

FIG. 2 is a diagrammatic arrangement of a typical apparatus suitable for applying a second or intermediate coating to a paper web, and which may be used as an alternative for applying the first or prime coating.

FIG. 3 is a diagrammatic illustration of a typical supercalender.

FIG. 4 is a diagrammatic arrangement of a typical apparatus suitable for applying the final or top coating to a prime coated paper web.

Referring to the drawings, the reference numeral 10 indicates a newly formed paper web, and as it leaves the drying drums 11 of the paper machine it continuously passes through the machine calender 12 and to the size press rolls 1313. Although the size press rolls 13 are shown to be horizontally aligned, it will be understood that although not shown, they can be vertically aligned.

As the web 10 passes between the rolls 1313 the opposed faces of the web are coated with aqueous mineral pigment-binder composition 14, the nip of the rolls being regulated to press the coating onto the Web and leave a metered amount thereon. The coated web then is dried by passing over the drier drums 15.

Typical examples of coating composition for this first step are the following, in parts by weight of solids:

EXAMPLE 1 #2 coating clay Enzyme converted corn starch 30 EXAMPLE 2 #2 coating clay 20 Precipitated C CO 40 Enzyme converted corn starch 35 EXAMPLE 3 #1 coating clay 70 Precipitated C CO 30 Hydroxyethyl corn starch 30 EXAMPLE 4 Clay 60 C CO precipitated 40 Starch, enzyme converted 35 Glyoxal 1.2

These prime coating compositions are made up with water to provide a solids content of from about 15 to about 45% by weight and preferably from about 30 to about 40%. The two side coat Weight can be from about 2 to about 12 pounds, and preferably from about 6 to about 10 pounds per ream of 3,300 square feet.

In lieu of applying the prime coat with a size press, it can be applied by means of an imprint type roll coater such as the type known as the Massey or Consolidated process diagrammatically shown by FIG. 2. Here the paper web 10 as it leaves the drier drums 11 of a paper machine in a continuous papermaking process, passes from the machine calender 12 to between the applicator rolls 16-16 where the opposed faces of the web 10 are coated with coating composition 17 which is transferred thereto in metered amount from the gate rolls 19 and through the transfer rolls 18. The coating is then dried by means of the dried drums 15.

It is to be further understood that coating means of the roll or imprint type other than the aforementioned Massey or Consolidated roll coater can also be uzed as well as smoothing bar and reverse roll coaters of various designs, such as those outlined in the Technical Pulp and Paper Industries Monograph Series #28, Pigmented-Coating Processes for paper and board, capable of applying suitable or equivalent levels of aqueous mineral pigmentbinder compositions similar to those herein described.

The coating composition 17 can be the same as the coating composition 14 previously described, a particularly suitable, water-resistant, composition for this Massey coating being as follows in parts by weight of solids:

EXAMPLE 5 Clay 45 C precipitated 40 TiO anatase 15 Casein 8 Butadiene-styrene latex 9 Ammonium stearate 0.6

When a first and intermediate coating are applied they can be applied in succession using the same arrangement of apparatus for each, or in the alternative by a combination of the arrangements of apparatus of FIGS. 1 or 2, or others as noted hereinbefore, either being first. When such second or intermediate coating is employed, it is desirably composed of a composition illustrated by the following examples in parts by weight of solids:

EXAMPLE 6 #2 coating clay 70 Precipitated C CO 25 TiO 5 Enzyme converted corn starch 22 Ammonium stearate 0.6

EXAMPLE 7 #1 coating clay 50 Prepicitated C CO 40 TiO Hydroxyethyl corn starch Ammonium stearate 0.5

EXAMPLE 8 #1 coating clay 60 Precipitated C CO 35 TiO 5 Hydroxyethyl corn starch 18 Styrene butadiene latex 5 Ammonium stearate 0.5

These second coat formulations are desirably made up with water to a solids content of from about 45 to about 50% by weight, and preferably from about 50 to about 55% by weight. The two side coat weight applied here is from about 4 to about 12 pounds, and preferably from about 6 to about 9 pounds per ream of 3,300 square feet.

After being prime coated with single or double coating as hereinbefore described, the paper web, after leaving the drier drum sections 15, is wound up and thereafter subjected to supercalendering. As diagrammatically indicated in FIG. 3, the paper web 10 passes from unwind roll 20 through the stack of supercalender rolls, a number of which are steel, as at 21, and wherein a number of them such as at 22 are provided with a resilient covering of fibrous material whereby the web 10 in passing between these rolls, and over the fly rolls 23, is densified and smoothed. Although not shown, it will be understood that the series of rolls 21 and 22 are journaled 1n mountings slidably received in a standard, the lowermost roll in the stack being driven and the stack maintained under compression through hydraulic means exerted on the uppermost roll, as is well understood. As previously indicated, the web 10 is here subjected to conventional supercalendering pressures, the calender stack being loaded so as to produce a nip pressure of from about 1,000 to about 1,700 pounds per linear inch, the preferred range being from about 1,200 to about 1,500 pounds per linear inch, after which it is wound up on the wind-up roll 24 for further processing.

As shown in' the details of FIG. 4, the web 10 is unwound from the roll 24 and the opposed sides thereof are subjected to a final or top coat. Here the web 10 is caused to pass around the back-up roll 25 whereat a layer of coating composition 26 is applied by means of the applicator roll 27, and shortly thereafter excess coating is removed therefrom by means of the flexible metal blade 28. This blade coating step is variously termed trailing blade coating, inverted blade coating, or flooded nip type inverted blade coating. In lieu thereof, although not shown, instead of the flexible metal blade 28 the doctor- 1ng may be practiced by means of a jet of compressed air extending across the width of the web sometimes termed an air knife or air brush, also well known in the art.

As a further alternative, although not shown, this top coating may be applied by passing the web 10 while in contact with the applicator roll 25 through a pool of coating composition maintained in a trough, the lower or bottom face of which is defined by a flexible metal doctor blade, well known in the art and described in Dickerman et al. United States Patent 2,949,382, sometimes known as the puddle type trailing blade coater.

The coated face of the doctored web then is subjected to drying by passing through a plurality of drying units such as the infrared unit 29 and the drum driers 30, aided by the high-velocity air hood 31. The one side coated web 10 then passes over a similar arrangement of apparatus indicated by prime reference numerals, to coat the opposed side and is then passed to wind-up reel in finished condition.

Illustrative of the coating compositions which are suitably applied as this final or top coating are the following in parts by weight of solids:

Acrylic latex Casein Although air knife doctoring or metering as a final or.

top coating step, in lieu of flexible metal blade doctoring, employs formulations suitable to the foregoing Examples 9 to 11, they are generally made up with water to be lower in solids. A typical formulation suitable for such application in parts by weight of solids is as follows:

Clay 50 CaCO precipitated 40 TiO anatase 10 Butadiene-styrene latex The foregoing is desirably made up with water to about 30% solids and is applied in a weight of approximately 8 pounds per ream.

Although we have shown the doctor type of coating in the final or top coat, it may be employed as well for applying the prime coat or for applying an intermediate coat when the latter is employed. However, suitable sequences are the following:

(A) Size press coating; supercalendering; doctored top coating.

(B) Imprint type roll coater; supercalendering; doctored top coating.

(C) Size press coating; imprint type roll coating supercalendering; doctored top coating.

The resulting sheet has a dull or low-gloss coating and on printing shows a sharp contrast between the ink gloss and the paper background with a substantial improvement in ink-holdout compared with hitherto conventionally processed sheets. The following illustrate some of the properties of sheets prepared in accordance with our process before and after coating, employing a blade coater in the final step:

Percent KdzN- 1 Weights given are per ream of 3,300 square feet.

We claim:

1. The method of coating a paper web which comprises applying to at least one surface of a forwardly moving paper web a plurality of coats of aqueous mineral pigment and binder containing coating composition, drying each coating after application, subjecting the web to supercalendering only prior to the application of the last coating, doctoring the last coating before drying, and recovering a coated paper of relatively low gloss surface and improved ink holdout character.

2. The process of claim 1 wherein the total number of applied coatings is two.

3. The process of claim 1 wherein the total number of applied coatings is three.

4. The process of claim 1 wherein the doctoring is accomplished by means of a flexible blade.

5. The process of claim 1 wherein the doctoring is accomplished by means of an air jet.

6. The process of claim 1 wherein both sides of the paper web are coated as described.

7. The process of claim 1 wherein the web is subjected to a supercalender roll nip pressure of from about 1,000 to about 1,700 pounds per linear inch.

8. A product formed in accordance with the process of claim 1.

9. The method of coating a paper web which comprises applying to at least one surface of a forwardly moving paper web at least one coat of aqueous mineral pigment and binder containing aqueous coating composition, dry ing said coating after application, supercalendering said coated web surface to impart gloss thereto, applying thereover a final aqueous mineral pigment and binder containing coating composition, doctoring and then drying the latter coating, and recovering the coated web as the product of the process in the absence of further supercalendering.

References Cited UNITED STATES PATENTS 1,719,166 7/1929 Bradner 117-156 X 2,006,208 6/1935 Bradner 117-64 2,214,565 9/1940 Montgomery et al. 11764 2,395,992 3/1946 Clark 117--65.2 2,656,286 10/1953 Fisher et a1 117-76 X 2,937,955 5/1960 Loomer 1l783 X 2,949,382 8/1960 Dickerman et al. 11776 X 3,268,354 8/1966 Hain 1l764 WILLIAM D. MARTIN, Primary Examiner.

M. LUSIGNAN, Assistant Examiner. 

